Thermionic tube having novel heater and cathode



G- W. BAKER Aug. 1:966

THERMIONIC' TUBE HAVING. NOVEL HEATER AND CATHODE Filed June 29, 1962 HEATER TAB INVENTOR GEORGE w. BAKER Y B e: M

ATTORNEYS.

United States Patent 3,265,924 THERMIQNIC TUBE HAVING NUVEL HEATER AND CATHODE George W. Baker, Stamford, 60am, assignor to York Research Corporation, Stamford, Coma, a corporation of Delaware Filed June 29, 1962, Ser. No. 2li6,365 (Ilaims. (Cl. 313-337) This invention relates to an improved thermionic electron tube of the hot cathode type and more particularly relates to a thermionic tube having a novel heater and a novel cathode.

In devising electrical circuits which are to respond quickly to applied signals, it is desirable to employ electron tubes in which the cathode reaches its operating temperature in as short a time interval as possible. The time required to heat a cathode to its operating temperature, herein called the heating time depends in large part on the volume per unit of surface area of base metal used in the cathode. The volume of base metal cannot be decreased arbitrarily since the cathode must have sufficient strength so as to be strong and stiff and thereby support itself during operation.

The heating time may be shortened, however, by providing a cathode which will dissipate more heat per unit surface area at its normal operating temperature. In the case in which the base material for the cathode is the conventionally used nickel alloy cathode, shortening of heat ing time by increasing the heat dissipated per unit area is limited simply because a higher operating temperature is required; the maximum operating temperature of the cathode is limited by evaporation of material from the coating of the cathode and the resulting short life of the tube.

An object of this invention is to provide an electron tube having a hot cathode which is heated quickly to its operating temperature.

A further object of this invention is to provide a coated cathode for an electron tube which is adapated to operate at temperatures substantially higher than previously possible for coated cathodes.

A further object of this invention is to provide a coated cathode for high temperature operation in which the cathode metal has a relatively low heat capacity per unit volume.

A still further object of this invention is to provide an improved heater for quickly heating my novel cathode.

Still another object of this invention is to provide an efiicient heater for use in thermionic electron tubes.

In general, the foregoing objects are accomplished by providing a cathode of an alloy containing about 92 percent platinum and 8 percent tungsten. Further, the novel heater used in conjunction with my novel cathode features the use of parallel strands of a heating wire folded back and forth upon itself many times thereby providing an increased effective radiating area per unit volume of heating wire.

Other objects and advantages will be pointed out or will occur to those skilled in the art from a reading of the following specification in conjunction with the accompanying drawings. In said drawings, which show, for illustrative purposes only, a preferred form of the invention:

FIG. 1 is a cross-sectional top view of the electron tube of this invention showing the position of the elements therein;

FIG. 2 is a greatly enlarged front sectional view through a plane 2-2 of FIG. 1 showing the configuration of the elements of the tube.

Referring now to FIG. 1 there is shown a thermionic electron tube having an outer envelope 10, a hollow cath- Patented August 9, 1966 ode 11, a control grid 12 and an anode 13. Heater means comprising wires 14 and 15 connected in parallel are positioned within cathode 11.

Cathode 11 comprises a sleeve, the base metal of which is formed of an alloy comprising approximately 92 percent platinum and 8 percent tungsten. Of course it is not necessary to limit the alloy of the metal to exactly 92 percent platinum and 8 percent tungsten by weight; however, it has been found that such proportion produces peculiarly improved performance.

It is intended that the coating on the cathode will be conventional, such as for example, alkaline earth oxides.

The novel cathode described has several new and desirable properties not possessed by the convention alloys used for the base metal of the said cathode. The heating time is substantially reduced since the volume of material per unit of surface area used for the cathode may be reduced by making the wall thinner; that is, the volume heat capacity (which is a measure of the quantity of heat required to raise a unit of surface area to a given temper-ature) of the base metal of the cathode is substantially reduced. Although the heating time has been substantially reduced, my novel cathode retains sumcient strength and stiffness when hot and may be used in a thickness of approximately 0.001 inch as compared with conventional nickel cathode having a thickness of 0.0025 inch. The decrease in volume heat capacity has been found to be approximately 40 percent as compared with the volume heat capacity of conventionally used nickel alloy cathode; or to state this advantage in a positive manner, my novel alloy may be considered as having approximately 60 percent of the volume heat capacity of nickel alloy cathode.

Summarizing thus far, the advantages apparent in my novel platinum-tungsten alloy cathode are first, it allows more heat radiation or dissipation per unit of surface area at a given temperature than the conventional alloy and second, it does not cause the coating material of the cathode to evaporate at a temperature at which a conventional alloy cathode would be required to operate for similar effectiveness. It is less active and has good life when operated at high temperatures in comparison with the conventional nickel cathode. Further the power radiated per unit of surface area is approximately twice that of the conventional alloy at the normal operating temperature; this provides an improvement in heating time by a factor of 2. Considering all of the factors just mentioned, the heating time is reduced by a factor of better than 8 to 1.

It is to be understood that my improved electron discharge device may utilize one or more control electrodes and may or may not be filled with gas depending upon the type of operation desirable.

In a conventional hot cathode tube, the temperature of the heater increases quickly compared with that of the cathode. When using my novel cathode it is apparent that the limitation in the heating time of the cathode1 fmay be caused now by the heating time of the heater itse The heating capacity of such heaters may be increased by either increasing the current through the heating wire or by reducing its cross-sectional areas when a constant voltage is used. However, this imposes structural requirements on the material of the heater which may in practice become impossible. If the strength of the heater wire is increased while at the same time a higher heating current is employed, necessarily an increase in the volume of the heater wire occurs. This decreases the efiiciency since the heat radiating surface of the wire is proportional to the diameter of the wire (the perimeter being directly proportional to the diameter) while the weight or volume of the wire is proportional to the square of the diameter.

My novel heater is designed to operate primarily with a heating current of 150 milliamperes and the heating time will be sufficiently short to provide a satisfactory heater for use with my novel cathode. The heater comprises tungsten wires 14 and 15 coated with a conventional insulating material which are folded back and forth upon themselves a plurality of times in a closely spaced pattern for a length approximately equal to a length of the cathode. The heater is positioned within the cathode and comprises two or more identical wires connected together in parallel.

The heater wires generally have a circular cross-section. It is important that the wires are not wound into a coil since the radiation from one turn of the coil interferes with the radiation of the adjacent turn. The effective radiating area is reduced and consequently the ratio of volume to radiating area is poor. The folds in heater 14 consist of two or more strands connected in parallel and in this manner I provide a greater heating area for the same power dissipation than previously obtained. It does not matter if some of the respective folds touch one another and in fact this may be expected. Since the wire is provided with an insulating coating no loss of operation or effectiveness occurs when one wire touches the other. The insulating coating I use is conventional, such as alumina.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that the description is made only by way of example and not as a limitation of the scope of the invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. An electron discharge device comprising an outer envelope,

a heater element therein being formed of tungsten and having an insulating surface thereon,

said heating element having two or more strands connected in parallel and formed into a plurality of folds,

a cathode base therein,

said cathode base being formed of "an alloy of metal comprising approximately 92 percent platinum by weight and the remaining part being approximately 8 percent tungsten.

2. The electron discharge device of claim 1 in which said cathode base has a coating thereon,

said coating being selected from one of the alkaline earth oxides.

3. The electron discharge device of claim 1 in which said envelope is substantially filled with gas.

4. The electron discharge device of claim 3 including a control electrode.

5. An electron discharge device comprising a substantially evacuated outer envelope,

cathode base means,

means for heating said cathode,

said cathode base means being formed of a platinum tungsten alloy having about 92 percent platinum and 8 percent tungsten by weight,

6. For use in an electron discharge device, a cathode base element formed of an alloy comprising approximately 92 percent platinum by weight and approximately 8 percent tungsten by weight.

7. An article of manufacture, a cathode base element formed of an alloy comprising approximately 92 percent platinum by weight and approximately 8 percent tungsten by Weight.

8. An electron discharge device comprising an outer envelope,

a heater element therein and a cathode base,

said cathode base being formed of an alloy comprising approximately 92 percent platinum by weight and approximately 8 percent tungsten by weight,

a coating on said cathode base,

said coating being selected from one of the alkaline earth oxides,

a control electrode,

said heater element comprising two or more folded tungsten wires connected in parallel having a length equal approximately to the length of said cathode base element and an insulation coating on said heating element.

9. As claim 8 in which said outer envelope is filled with gas and having a control electrode therein.

10. An electron discharge device comprising an outer envelope,

a heater element therein being formed of tungsten and having an insulating surface thereon,

said heating element having at least one strand formed into a plurality of folds, a cathode base therein, said cathode base being formed of an alloy of metal comprising approximately 92% platinum by weight and the remaining part being approximately 8% tungsten.

References Cited by the Examiner UNITED STATES PATENTS 1,407,525 2/1922 Fry -172 1,850,809 6/1923 Robinson 117223 2,164,913 7/1939 Goodchild 313-341 X 2,473,504 6/1949 Boddie 313-263 X 2,813,227 11/1957 Sweet 313337 X JOHN W. HUCKERT, Primary Examiner.

GEORGE N. WESTBY, Examiner.

L. ZALMAN, Assistant Examiner. 

10. AN ELECTRON DISCHARGE DEVICE COMPRISING AN OUTER ENVELOPE, A HEATER ELEMENT THEREIN BEING FORMED OF TUNGSTEN AND HAVING AN INSULATING SURFACE THEREON, SAID HEATING ELEMENT HAVING AT LEAST ONE STRAND FORMED INTO A PLURALITY OF FOLDS, A CATHODE BASE THEREIN, SAID CATHODE BASE BEING FORMED OF AN ALLOY OF METAL COMPRISING APPROXIMATELY 92% PLATINUM BY WEIGHT AND THE REMAINING PART BEING APPROXIMATELY 8% TUNGSTEN. 